1. Field of the Invention
The present invention relates to heat spreaders for semiconductor devices to prevent a temperature rise due to heat generated by the semiconductor devices. In addition, the present invention relates to semiconductor devices and packages with the heat spreaders.
2. Description of the Related Art
To facilitate heat dissipation from semiconductor devices, for example, a semiconductor package with a combination of a high thermal-conductivity ceramic base material and a resin wiring substrate such as a printed circuit board has been proposed in Japanese Unexamined Patent Application Publication No. 10-275879. This semiconductor package includes a semiconductor device mounted on the bottom surface of an aluminum nitride heat spreader and a resin wiring substrate bonded around the semiconductor device. This resin wiring substrate has a wiring layer wired to a signal wiring of the semiconductor device. Semiconductor packages of this type are expected to, for example, meet high power-consumption semiconductor devices and achieve a low-resistance, high-density signal wiring and a low-cost package.
In these semiconductor packages, however, a large semiconductor device of, for example, 20 mm by 20 mm requires a large aluminum nitride substrate. When a metal radiating fin is bonded entirely on the top surface of such a large aluminum nitride substrate, the aluminum nitride substrate may cause defects such as cracking during heat cycles due to the difference in thermal expansion coefficients between the aluminum nitride substrate and the metal radiating fin.
Semiconductor packages using high thermal-conductivity ceramics, such as the above aluminum nitride substrate, or a metal plate, such as a copper plate, as a heat spreader have been used in practice as packages for meeting high power-consumption semiconductor devices. Nevertheless, these semiconductor packages have difficulty in meeting a further increase in the power-consumption of the semiconductor devices. In addition, a heat spreader made of only high thermal-conductivity ceramics decreases the reliability of bonding of a heat sink or a radiating fin in a face-down structure, which is supposed to provide a high heat-dissipation package. On the other hand, a heat spreader made of, for example, a copper plate decreases the reliability of mounting of the semiconductor devices.
FIG. 8 shows a sectional view of an example of known semiconductor packages with a heat spreader. A semiconductor device 102 is mounted on a heat spreader 101, which is bonded over an opening of a ceramic package body 103 such that the semiconductor device 102 is disposed inside the package body 103. A ceramic cover 104 is disposed on the other opening of the package body 103 to seal the semiconductor device 102 in this package.
Such a heat spreader has so far been made of, for example, a composite material of copper and tungsten, aluminum nitride, or silicon carbide. Japanese Unexamined Patent Application Publication No. 9-129793 also discloses a heat transfer plate for semiconductor packages.
The heat dissipation characteristics of these known heat spreaders and semiconductor packages using such heat spreaders seem to have been improved to the limit in terms of the materials used and their structures. Therefore, further improvement of the heat dissipation characteristics is difficult. As a result, the processing speed, output, and degree of integration of semiconductor devices must be controlled to suppress the temperature rise of the packages.